Circulating Hsp70 - a tumor biomarker for lymph node metastases and early relapse in thoracic cancer

Background : Heat shock protein 70 (Hsp70) which is frequently overexpressed in many different cancer types is also present on the plasma membrane of tumor but not normal cells. The intensity of membrane-expressed Hsp70 (mHsp70) is associated with disease progression and treatment resistance. It has also been shown that Hsp70 can be actively released into the circulation by mHsp70 positive, viable tumor cells in the form of extracellular lipid microvesicles expressing mHsp70, the levels of which might therefore act as a potential biomarker for tumor aggressiveness in lung malignancies. Methods: Extracellular Hsp70 (eHsp70) was measured in the plasma of patients with non-small cell lung cancer (n=178, NSCLC) and lung metastases of extrathoracic tumors (n=35) prior to surgery using the Hsp70-exo ELISA which detects microvesicle-associated Hsp70 and the patient`s immunophenotype was determined by flow cytometric analysis of the corresponding peripheral blood lymphocytes. Results: eHsp70 values were significantly higher in patients with NSCLC than in healthy individuals, with no differences between adeno and squamous cell carcinomas. Levels of circulating Hsp70 gradually increased from early stage to metastatic disease, and patients with lymph node metastases in surgically treatable NSCLC had significantly higher eHsp70 levels than nodal negative patients. In all tumor stages, total lymphocyte counts were significantly reduced and Treg counts were increased compared to healthy controls. Lower CD4+ T helper cell and higher CD3-/CD56+/CD94+/CD69+/NKp30+/NKp46+ NK cell ratios were only found in patients with thoracic metastases of other primary tumors. An early relapse after complete resection with curative intent correlated with significantly elevated eHsp70 levels, which were measured prior to surgery, in all lung cancer patients. Conclusions: In summary, we propose circulating eHsp70 levels as a predictive biomarker for the presence of lymph node metastases and early therapy failure in patients with thoracic malignancies.